|Your best bet is to boot to a Vista DVD and remove any partitions that contain the virus/rootkit/malware |
From there you can try a startup repair: http://windows.microsoft.com/en-us/...
You can also try to repair the OS:
1. boot from the Vista DVD
2. Windows Setup will start loading till language and location selection screen appears.
3. Adjust Language to install, Time and currency format, and Keyboard or input method options, click Next,
4. Main Windows Vista setup screen appears, click on the Repair your computer option,
5. This will bring you to a new screen where the repair process will look for all Windows Vista installations on your computer,
6. When Windows Vista detects OS installed you will be presented with the System Recovery Options dialog box,
7. Select the Vista installation you would like to repair (usually only one is shown) press the Next button to continue.
8. Repair process will start, please note that if repair process detects any problem it will automatically starts Startup Repair